Exposing device for copying apparatus

ABSTRACT

An exposing device for copying apparatus wherein a photoreceptive surface and a reflector are moved, while a copying lens and an original to be duplicated remain stationary, for exposing the photoreceptive surface to an optical image of the original by a slit system for the purpose of producing a duplicate of the original. The reflector comprises two reflecting surfaces meeting at a 90* angle, along a line of juncture lying in a plane oriented at 45* to the optical axis of the lens. It is interposed between the copying lens and photoreceptive surface and moves at a rate which is one-half the rate of movement of the photoreceptive surface in the direction of movement of the photoreceptive surface.

United States Patent Suzuki [54] EXPOSING DEVICE FOR COPYING APPARATUS [72] Inventor: Shigeru Suzuki, Yokohama, Japan [73] Assignee: Ricoh Co. Ltd., Tokyo, Japan [22] Filed: Aug. 10, 1971 [21] Appl. No.: 170,462

[30] Foreign Application Priority Data Post et al ..355/8 1451 Oct. 10,1972

Primary Examiner-Samuel S. Matthews Assistant Examinerl(enneth C. Hutchison Attorney-Henry T. Burke et al.

[57] ABSTRACT An exposing device for copying apparatus wherein a photoreceptive surface and a reflector are moved, while a copying lens and an original to be duplicated remain stationary, for exposing the photoreceptive surface to an optical image of the original by a slit system for the purpose of producing a duplicate of the original. The reflector comprises two reflecting surfaces meeting at a 90 angle, along a line of juncture lying in a plane oriented at 45 to the optical axis of the lens. It is interposed between the copying lens and photoreceptive surface and moves at a rate which is one-ha1f the rate of movement of the photoreceptive surface in the direction of movement of the photoreceptive surface.

6 Claims, 10 Drawing Figures PATENTEDUBT 10 I972 SHEET 1 [IF 4 INVENTOR. J/I/GEEU suzu/w 4 TTOEA/Ek' SHEET 2 [IF 4 FIG.3

INVENTOR. SH/GEPU SUZUK/ ATTOIQ/WE) PAIENTEDocr 10 m2 SHEET 3 BF 4 INVENTOR. SH/GEEU SUZUK/ M ATTORNEY PAIENIEMM 10 I912 3. 697, 166

SHEET U 0F 4 INVENTOR SH/GEAZ/ SUZUK/ BACKGROUND OF THE INVENTION This invention relates to apparatus for producing copies of documents, pictures and other subjects (herein generically termed originals), wherein a photoreceptor is exposed to an optical image of the original to be copied. More particularly, the invention relates to exposing devices in such apparatus, i.e., devices for exposing the photoreceptor to the optical image. In a specific sense, the invention relates to new and improved optical exposing devices of the so-called slit exposure type.

For purposes of illustration, reference may be made to electrophotographic copying systems in which the photoreceptor or photoreceptive surface is a photoconductive surface on which an electrostatic latent image may be established by exposure to an optical image. Subsequently the latent electrostatic image may be developed, and converted to a visible image, as by application of a toner to the surface bearing the latent image. In certain types of electrophotographic copying systems, the photoconductive surface is a surface of a specially pre-treated sheet of copy paper or the like which, when developed, becomes a permanent copy of the original. In other systems (e.g., xerographic systems), the photoconductive surface is a seleniumcoated drum or other photoconductively coated transfer surface from which the developed images may 'be transferred to a recording substrate such as a sheet of ordinary paper. These and other electrophotographic copying systems are examples of some of the types of copying apparatus in which the present invention may be used.

For copying operations such as the foregoing, it has been found advantageous to effect exposure of the photoreceptive surface to the optical image of the original by means 'of slit exposure techniques, wherein successive portions of the surface are exposed to successive slit-shaped portions of the image until the exposure has been completed. There are a number of known exposing devices of the slit exposure type for copying apparatus and some of them have been put to practical use. In one type of device, an original and a photoreceptor are maintained in a predetermined relationship and both move with respect to a stationary copying lens. In another type of device, a copying lens system comprising a lens and a reflector moves with respect to an original and a photoreceptor which remain stationary. A still further type of device uses at least two reflectors which move together with a photoreceptor while an original and a copying lens remain stationary. In yet another type of device, a copying lens and a photoreceptor move with ,respect to an original which remains stationary.

All the exposing devices of the prior art have disadvantages and problems that have to be obviated. For example, devices wherein the photoreceptor is exposed to an optical image of the original while .the latter is moving have disadvantages in that this device is the time-consuming because the original which moves for exposing the photoreceptor to an optical image thereof has to be returned to its initial position, the device does not lend itself to use for producing duplicates of original papers which are rather voluminous or. an original of relatively heavy weight, and the device must be provided with means for moving the original at an accurate rate.

Devices of the type in which the photoreceptor fed to the copying apparatus is stopped at an exposing position and exposing means moves with respect to the stationary photoreceptor has many disadvantages. This device does not lend itself to use for high speed copying in which duplications are continuously produced because the photoreceptor must be stopped in the exposing position. The device must use photoreceptor conveyance control means of complex construction for stopping and moving the photoreceptor. The device is not fit for a high speed copying operation because exposing means of great bulk comprising a lens and a reflector must bemoved. Light intercepting means for preventing unnecessary light from reaching the photoreceptor should be provided. The device is time-consuming because the exposing means must be moved in reciprocating motion. When illumination means is provided in the exposing means for illuminating the original, power feed means of complex construction for the moving illumination means must be used.

The type of device in which the photoreceptor and reflectors move with respect to the original which remains stationary offers the advantage of being able to carry out copying continuously at high speed due to the fact that exposing is carried out while copy sheets are moved. However, at least two reflectors must be moved at different rates which are controlled to be maintained in a predetermined relation in this device; hence the reflector movement control means used should be highly precise and accurate in construction and operation, and naturally its construction becomes complex. Besides, it is necessary to move one reflector which is associated with the original throughout the entire length of the original, so that it is required to provide a space of large area in the apparatus for permitting the movement of the reflector. Moreover, this device is time-consuming because the reflector must be moved in reciprocating motion for a distance corresponding to the length of the original.

SUMMARY OF THE INVENTION The present invention contemplates the provision of a new and improved slit-type exposing device wherein a stationary copying lens focuses an image of a stationary original on a moving photoreceptive surface by means of a moving reflector. More particularly, the invention contemplates the provision of movable reflector means comprising two reflecting surfaces meeting along a line of juncture (herein sometimes termed the ridge of the reflector) at an angle of to each other. The reflector is disposed intermediate the lens and the focal plane of the lens with the line of juncture lying in a plane oriented at 45 to the optical axis of the lens. Means are provided for moving the reflector in such manner that the line of juncture undergoes translation in the lastmentioned plane, for directing successive portions of the image to a fixed slit-shaped locality in the focal plane of the lens, where the photoreceptive surface is disposed. The photoreceptive surface moves in the same direction as the reflector means during exposure, but at a faster rate (e.g., twice as fast as the reflector means) so that successive portions of the photoreceptive surface are exposed to the successive portions of the image directed to the slit-shaped locality, which may be defined as a slit by suitable masking means or the like. Further, in accordance with the invention, means may be provided for effecting angular displacement of the reflector means about an axis substantially coincident with the line of juncture at least adjacent a terminal portion of the path of reflector movement.

The exposing device for copying apparatus according to this invention is similar to the last-mentioned conventional device in that exposing is carried out while a photoreceptor and a reflector move with respect to a stationary original. However, the device according to this invention differs from the device of the prior art by the fact that, whereas the prior art device uses at least two reflectors which are moved at controlled different rates and one of the two reflectors should be moved at least a distance corresponding to the length of the original, in the present invention, one reflector comprising two reflecting surfaces which are connected together to operate as a unit has only to be moved a distance corresponding to substantially onehalf the length of the original. Accordingly, in the present invention, the reflector moves in reciprocating motion a small distance at a rate which is one-half the rate of movement of the photosensitive sheet. Thus, this invention obviates the disadvantages of the prior art device of similar type while retaining its advantages.

Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DIQAWINGS FIG. I is a perspective view, somewhat schematic, of an exposing device comprising one embodiment of this invention;

FIG. 2 is a plan view of the device shown in FIG. 1;

FIG. 3 is a schematic viewin explanation of this invention showing the slit optical image projected onto the reflector when the device is seen from-the copying lensside;

FIG. 4 is a fragmentary schematicview of FIG. 3 in which the slit optical image is shown in lines;

FIG. 5 is a schematic perspective view showing the relative positions of the reflector and the slit for carrying out exposing which is associated with the reflector;

FIG. 6 is a perspective view of the reflector intended to explain the function of the reflector used with the exposing device according to this invention;

FIG. 7a and 7b are schematic optical diagrams in explanation of the pivotal movement of the reflector carried out in the terminal zone within the range of movement thereof so as to improve the performance of the device according to this invention;

FIG. 8 is a side view of reflector pivoting means showing one from of such means: and

FIG. 9 is a plan view of the means of FIG. 8.

DETAILED DESCRIPTION In FIG. 1, an original 1 to be duplicated is placed on a transparent plate (not shown) secured to the top of the copying apparatus in the same manner as in conventional copying apparatus, with the upper surface of the original 1 to be copied facing downwardly. Disposed below the transparent plate is means for determining the direction in which the image of the original faces, such means being shown as a reflector 2 which is inclined substantially at an angle of '45 and secured to an immovable part of the copying apparatus (reflector 2 may be replaced by other forms, arrangements and numbers of reflectors). The original 1 to be duplicated is illuminated by suitable illumination means such that its surface is illuminated with uniform brightness. The illuminated original 1 is copied by a copying lens 3 onto a photoreceptor comprising a photosensitive sheet, subsequently to be described. While a photosensitive sheet that may be developed to constitute a copy of the original will be referred to in the following description, other forms of photoreceptive surface (such as. a selenium-coated drum, as in xerography) may be exposed by the present device.

The copying lens 3 is secured to an immovable part of the copying apparatus and placed intermediate between the original 1 and the path of movement of the photosensitive sheet 5 which are spaced apart from each other (along the optical path defined by reflectors 2 and 4) a distance corresponding to twice the focal length of the copying lens 3.

A reflector 4 comprising two reflecting surfaces A and B connected to each other and disposed at an angle of relative to each other is arranged such that a line of juncture (ridge 4AB of reflector 4) at which the reflecting surfaces A and 8 meet is disposed in a plane P inclined by 45 with respect to the optical axis of the copying lens 3. The reflector 4 is movably supported by suitable moving and support means (not shown in Fig. 1) so that it moves up and down in translating motion while the line of juncture or ridge 4AB thereof is disposed in the plane P which is disposed intermediate between the copying lens 3 and the focal plane thereof.

Assuming that there is an elongated zone a, b, c and d at one marginal portion of the original 1 which is disposed crosswise thereof, the light from the point a will be reflected by the reflector 2 and reach the reflecting surface A after passing through the copying lens 3. It will be reflected by thereflecting surface A at a point a 1 thereon and directed toward the reflecting surface 8', and it will be focused on a point a 3 after being reflected by the reflecting surface B at a point a 2 thereon. Similarly, the light from the point b willbe focused on a point b 3 after passing through the copying lens 3 and being reflected by the reflector A at a point b 1 thereon and by the reflector B at a point b thereon. The light from the point c will be reflected by the reflecting surface B at a point c and by the reflecting surface A at a point c after passing through the copying lens 3 before being focused on a point 0 The light from the point d .will be focused on a point (i after passing through the copying lens 3 and being reflected by the reflecting surfaces B and A at points d, and d, respectively.

The reflector 4 is so positioned that if it is moved upwardly from the position shown in FIG. 1 to a broken line position 104 in the same figure, a distance equal to about half the length of the original to be copied, an elongated zone w, x, y and z at the other marginal portion of the original 1 will form its image in the zone a;, b;, c and d The reflector undergoes such movement in the same direction as the direction of advance of the photosensitive sheet, perpendicular to the line of juncture. More specifically, the light from the point w will be reflected first by the reflector B at a point w thereon and then by the reflector A at a point w thereon before being focused on the point a Similarly, the light from the point x will be reflected by the'reflectors B and A at points x, and x, respectively thereon before being focused on the point b,,. The light from the point y'will be reflected by the reflectors A and B at points y, and y; respectively thereon before being focused on the point a while the light from the point x will be be focused on the point d after being reflected by points z, and z, on the reflectors A and B respective ly.

Accordingly, it will be evident that if the reflector 4 is moved to its broken line position 104 along a vertical tioned below the ridge 4AB and its left end plane at a rate which is one-half the rate of movement in spite of the movement of the reflector 4 from its solid line position to its broken line position 104. This phenomenon is accountedfor by the following fact: If the light incident on one (C) of the reflecting s'urfaces C and D connected to and disposed at an angle of 90 relative to each other as shown in FIG. 6 emerges from the other reflecting surface B after being reflected thereby, a plane M in which the incident light R, is disposed is parallel to a plane N in which the emerging light R is disposed (the lines at which the planes M and N are connected to the reflecting surfaces C and D respectively are parallel to the line of juncture or ridge of the reflector). Accordingly,'light incident on the reflecting surface C and disposed in a plane which intersects the surface C emerges from a plane intersecting the reflecting surface D and disposed parallel to the aforementioned plane intersecting the reflecting surface C. a g

The manner in which the zones a, b, c andd and w, x, y, and z are projected onto the two reflecting surfaces A and B by the copying lens will be explained with reference to FIG. 3. When the reflector 4 is in its lowermost position, a first image a b 0 and d of the zone a, b, c and d is formed such that the image is inclined with respect to the ridge 4AB and disposed with its rightend portion being positioned below the ridge 4AB and its left end portion being positioned above the ridge 4AB, and a second image a b 0 and d, thereof is formed such that the image is inclined with respect to the ridge 4AB and disposed with its right end portion being positioned above the ridge 4AB and its left end portion being disposed below the ridge 4AB, so that the two images intersect each other.

When the reflector 4 is disposed in its uppermost position, a first image w,, x,, y, and Z] of the zone w, x, y and z is formed such that the imageis inclined with respect to the ridge 4AB and disposed with its right end portion being positioned above the ridge 4AB and its left end portion being positioned below the ridge 4AB, and a second image W,, X,, y, and 2, thereof is formed such that the image is inclined with respect to the ridge 4AB and disposed with its right end portion being posiportion being disposed above the ridge 4AB.

When the reflector is placedin a position in which ridge 4AB of the reflector 4 intersects the optical axis of the copying lens 3 or which is disposed midway between its uppermost position and its lowermost position, a first image and a second image of the zone of the copy 1 which is interposed between the zone a, b, c and d and the zone w,x, y and z are formed on the ridge 4AB in superposed relationship with each other.

As can be seen from the aforementioned description, the angle 0 formed by the first image and second image is increasingly reduced as the reflector moves nearer to the optical axis of the copying lens till the angle becomes zero when the reflector is disposed in a position in which the ridge of the reflector intersects the optical axis of the copying lens. As stated previously, the second image is formed in a position indicated by short lines a b c, and a even if the position of the reflector is varied as aforementioned.

FIG.'4 shows the relative positions of the first image and'second image on the reflector by assuming the zone w, x, y andzto be asingle line to facilitate explanation by drawing. A solid linerepresents the first image and a broken line the second image.

' paper used, so that'the optical flux reflected by the reflector 4 and useful for exposing can only be made to be incident on the photosensitive paper. The amount of exposure of the photosensitive paper 5 to light can be controlled by adjusting the spacing between an edge 7a of the member 7 and an edge 8a of the member 8, or by regulating the rate of movement of the photosensitive sheet. As will be understood, the slit is disposed substantially at the focal plane of lens 3.

The photosensitive sheet 5 is adapted to be continuously moved upwardly at constant rate by a pair of rollers 9 and 10 mounted above and below the slit. On the other hand, the reflector 4 is adapted to be guided by perpendicularly disposed guide rods 11 and 12 to move in the same direction as the photosensitive sheet 5 at a rate which is one-half the rate of movement of the photosensitive sheet.

As will be understood, such features as the positions vicinityof its uppermost position and lowermost position in its range of reciprocating movement. This is effective to increase the effective copying range of the copy sheet in the longitudinal direction thereof. This 'feature of the invention will be explained with reference to FIG. 7(a) and (b).

FIG. 7(a) schematically shows the range of movement of the reflector 4 in which its ridge moves in translating motion along a plane inclined by 45 with respect to the optical axis of the copying lens without changing its direction as described previously. The

' range of movement which is allowed to the reflector 4 is twice the distance d between a center line a of a slit 15 and the ridge 4AB. If the reflector 4 is moved away from the center line a distance greater than the distance d, the angle of incidence of light 13 on the reflecting surface A will become close to 90 and consequently the angle of emergence of light 14 leaving the reflecting surface B and directed toward the lower end of the center line 15a of the slit 15 will also become close to 90. In this condition, the light reflected by the reflecting surface B and reaching a lower end corner 15b of the slit 15 will not be available for exposing purposes, because the side 15b and the reflecting surface B are in contact with each other as shown.

FIG. 7(b) shows the angular displacement of the reflector 4 in the direction of the arrow a about its ridge while the reflector 4 moves a distance D which is greater than the aforementioned distance d. If the reflector 4 is angularly displaced as aforementioned in the terminal zone of'its movement, the angle of incidence of light 113 on the reflecting surface A will be smaller than that of the corresponding light 13 shown in FIG. 7(a) in spite of the fact that the reflector 4 moves the distance D which is greater than the aforementioned distance d of movement thereof in FIG. 7(a). Accordingly, light 16 reaching the lower end corner 15b will be available for exposing purposes.

It will be appreciated that if the range of movement of the reflector 4 is increased, the scope of duplication can be increased. As compared with the scope of duplication l-of the operation shown in FIG. 7 (a), the scope of duplication can be increased as indicated by D in FIG. 7(b) when the reflector is moved in pivotal motion.

FIGS. 8 and 9 show one example of means for moving thereflector 4 inwardly in pivotal motion in the terminal zone of its movement, although other types of means for pivotally moving the reflector may be employed. A reflector supporter 17a firmly holding the reflector 4 has attached to opposite ends thereof stub shafts 17a and 17b which are rotatably journalled by bearings 18a and 18b respectively which project from a slider 18.-It is essential that the shafts 17a and 17b should be attached to the supporter 17 such that center lines 170 and 17d thereof are disposed on an extension of the ridge 4AB of the reflector 4.

The slider 18 is formed on opposite ends thereof with projections 18c and 18d which loosely receive support rods 19 and 20 in holes formed therein respectively, so that the slider 18 is supported for sliding motion by the guide rods 19 and 20. The slider 18 has an arm l8e attached thereto in a position midway between the projections 18c and 18d. The arm l8e has secured thereto a wire 21 which is pulled upwardly and downwardly by reflector operating means which is coupled to photosensitive sheet feed means, whereby the reflector 4 can be moved upwardly and downwardly.

A pivotal arm 23 having a roller mounted at its free end is attached at its base to the shaft 17b of the reflector supporter 17. The roller 22 is maintained in pressing engagement with an edge 24a of a guide 24 which edge is inclined with respect to the support rod 20. The force with which the roller 22 is maintained in pressing engagement with the edge 24a stems from the weight of the reflector 4 and the supporter 17. However, the weight of the reflector 4 and supporter 17 does not produce a force which causes the shaft 17a and 17b to move in pivotal motion when exposing by a slit system is carried out by moving the reflector in a horizontal direction. It will be needless to say that, in such case, suitable means must be provided for bringing the roller into pressing engagement with the edge 24a, such as resilient means acting on the pivotal arm 23, for example.

In FIG. 8, if the reflector 4 is moved upwardly, the roller 22 will move pivotally together with the arm 23 in a clockwise direction aboutthe shaft 17b while the roller 22 moves in rolling motion on the edge 24a, so that the reflector will be angularly displaced inwardly. Conversely, if the reflector is moved downwardly, the roller 22 will be pushed outwardly by the edge 24a, so that the reflector will again be angularly displaced inwardly.

It is to be understood that the invention is not limited to the features and embodiments hereinabove specifically set forth but may be carried out in other ways without departure from its spirit.

What is claimed is:

1. In copying apparatus, in a device for exposing a photoreceptive surface to an optical image of an original to be copied, the combination comprising:

a. A copying lens, having an optical axis and a focal plane, for focusing'an optical image of an original on the focal plane; means for defining a slit at the local plane of said lens b. Movable reflector means, comprising two reflecting surfaces meeting along a line of juncture at an angle of to each other and disposed intermediate said lens and the focal plane thereof for reflecting portions of the image, said line of juncture lying in a plane oriented at 45 to the optical axis of the lens;

c. Means for effecting translational motion of said reflector means at a predetermined rate along a limited path while said line of juncturelies in said last-mentioned plane, so as to reflect a portion of said image onto said slit, and

d. Means for advancing a photo-receptive surface past said slit in the same direction as said reflector means at a predetermined rate substantially faster than the rate of movement of the reflector means, said photoreceptive means being disposed to receive portions of said image reflected by said reflector means to said slit-shaped locality.

2. A device as defined in claim 1, wherein the rate of movement of said photoreceptive surface is twice the rate of movement of said reflector means.

3. A device as defined in claim 1, further including means for effecting angular displacement of said reflector means, about an axis substantially coincident with said line of juncture, adjacent at least one extremity of said limited path.

4. In copying apparatus, a device for exposing a moving photoreceptive surface to an optical image of a stationary original to be copied, said device comprising:

a. A copying lens having an optical axis and a focal plane;

b. Means for delivering light from an illuminated fixed original to said lens for focusing of an optical image of the original on the focal plane;

c. Means for defining a fixed slit at the focal plane of the lens;

(1. Means for effecting translational motion of a photoreceptive surface at a first predetermined rate past said slit;

e. Movable reflector means comprising two reflecting surfaces meeting along a line of juncture at an angle of 90 to each other and disposed intermediate said lens and the focal plane thereof for reflecting portions of the image to the slit, said line of juncture lying in a plane oriented at 45 to the optical axis of the lens; and

f. Means for moving said reflector means such that said line of juncture undergoes translation in said last-mentioned plane at a second predetermined rate, slower than said first predetermined rate, in a 10 toreceptive surface passing the slit are respectively exposed to successive portions of the image reflected to the slit.

5. An exposing device for copying apparatus, com- 5 prising:

a. A copying lens; a reflector comprising two reflectb. Means for translating said reflector while maintaining the ridge thereof in said last-mentioned plane;

0. Means for advancing a photoreceptor in a the same direction as the movement of said reflector at a rate which is twice the rate of movement of the reflector, whereby the photoreceptor can be exposed through the slit.

direction parallel to the direction of movement of An exposing device as defined in claim 5 including the photo-receptive surface and perpendicular to means for f y displacing said reflector inwardly the line f juncture, for fl ti successive pop about the ridge thereof which serves as the center of tions of the image onto Said fixed slit saidlfirst and angular displacement in a terminal zone of the movesecond predetermined rates being respectively mam of the reflector selected so that successive portions of the pho- 

1. In copying apparatus, in a device for exposing a photoreceptive surface to an optical image of an original to be copied, the combination comprising: a. A copying lens, having an optical axis and a focal plane, for focusing an optical image of an original on the focal plane; means for defining a slit at the local plane of said lens b. Movable reflector means, comprising two reflecting surfaces meeting along a line of juncture at an angle of 90* to each other and disposed intermediate said lens and the focal plane thereof for reflecting portions of the image, said line of juncture lying in a plane oriented at 45* to the optical axis of the lens; c. Means for effecting translational motion of said reflector means at a predetermined rate along a limited path while said line of juncture lies in said last-mentioned plane, so as to reflect a portion of said image onto said slit, and d. Means for advancing a photo-receptive surface past said slit in the same direction as said reflector means at a predetermined rate substantially faster than the rate of movement of the reflector means, said photoreceptive means being disposed to receive portions of said image reflected by said reflector means to said slit-shaped locality.
 2. A device as defined in claim 1, wherein the rate of movement of said photoreceptive surface is twice the rate of movement of said reflector means.
 3. A device as defined in claim 1, further including means for effecting angular displacement of said reflector means, about an axis substantially coincident with said line of juncture, adjacent at least one extremity of said limited path.
 4. In copying apparatus, a device for exposing a moving photoreceptive surface to an optical image of a stationary original to be copied, said device comprising: a. A copying lens having an optical axis and a focal plane; b. Means for delivering light from an illuminated fixed original to said lens for focusing of an optical image of the original on the focal plane; c. Means for defining a fixed slit at the focal plane of the lens; d. Means for effecting translational motion of a photoreceptive surface at a first predetermined rate past said slit; e. Movable reflector means comprising two reflecting surfaces meeting along a line of juncture at an angle of 90* to each other and disposed intermediate said lens and the focal plane thereof for reflecting portions of the image to the slit, said line of juncture lying in a plane oriented at 45* to the optical axis of the lens; and f. Means for moving said reflector means such that said line of juncture undergoes translation in said last-mentioned plane at a second predetermined rate, slower than said first predetermined rate, in a direction parallel to the direction of movement of the photo-receptive surface and perpendicular to the line of juncture, for reflecting successive portions of the image onto said fixed slit, said first and second predetermined rates being respectively selected so that successive portions of the photoreceptive surface passing the slit are respectively exposed to successive portions of the image reflected to the slit.
 5. An exposing device for copying apparatus, comprising: a. A copying lens; a reflector comprising two reflecting surfaces connected to each other and disposed at an angle of 90* relative to each other to form a ridge, said reflector being arranged between said copying lens and the focal plane thereof such that the ridge of the reflector is disposed in a plane which is inclined by substantially 45* with respect to the optical axis of the lens; b. Means for translating said reflector while maintaining the ridge thereof in said last-mentioned plane; c. Means for advancing a photoreceptor in a the same direction as the movement of said reflector at a rate which is twice the rate of movement of the reflector, whereby the photoreceptor can be exposed through the slit.
 6. An exposing device as defined in claim 5 including means for angularly displacing said reflector inwardly about the ridge thereof which serves as the center of angular displacement in a terminal zone of the movement of the reflector. 